img2_13.py

import cv2.cv as cv
 
capture = cv.CaptureFromCAM(0)
 
width = int(cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FRAME_WIDTH))
height = int(cv.GetCaptureProperty(capture, cv.CV_CAP_PROP_FRAME_HEIGHT))
 
prev_gray = cv.CreateImage((width,height), 8, 1)
gray = cv.CreateImage((width,height), 8, 1)
 
prevPyr = cv.CreateImage((height / 3, width + 8), 8, cv.CV_8UC1) #Will hold the pyr frame at t-1
currPyr = cv.CreateImage((height / 3, width + 8), 8, cv.CV_8UC1) # idem at t
 
max_count = 500
qLevel= 0.01
minDist = 10
prev_points = [] #Points at t-1
curr_points = [] #Points at t
lines=[] #To keep all the lines overtime
 
while True:
    frame = cv.QueryFrame(capture)
    cv.CvtColor(frame, gray, cv.CV_BGR2GRAY) #Convert to gray
    output = cv.CloneImage(frame)
 
    prev_points = cv.GoodFeaturesToTrack(gray, None, None, max_count, qLevel, minDist)
    curr_points, status, err = cv.CalcOpticalFlowPyrLK(prev_gray, gray, prevPyr, currPyr, prev_points, (10, 10), 3, (cv.CV_TERMCRIT_ITER|cv.CV_TERMCRIT_EPS,20, 0.03), 0)
 
    #If points status are ok and distance not negligible keep the point
    k = 0
    for i in range(len(curr_points)):
        nb =  abs( int(prev_points[i][0])-int(curr_points[i][0]) ) + abs( int(prev_points[i][1])-int(curr_points[i][1]) )
        if status[i] and  nb > 2 :
            prev_points[k] = prev_points[i]
            curr_points[k] = curr_points[i]
            k += 1
 
    prev_points = prev_points[:k]
    curr_points = curr_points[:k]
    #At the end only interesting points are kept
 
    #Draw all the previously kept lines otherwise they would be lost the next frame
    for (pt1, pt2) in lines:
        cv.Line(frame, pt1, pt2, (255,255,255))
 
    #Draw the lines between each points at t-1 and t
    for prevpoint, point in zip(prev_points,curr_points):
        prevpoint = (int(prevpoint[0]),int(prevpoint[1]))
        cv.Circle(frame, prevpoint, 15, 0)
        point = (int(point[0]),int(point[1]))
        cv.Circle(frame, point, 3, 255)
        cv.Line(frame, prevpoint, point, (255,255,255))
        lines.append((prevpoint,point)) #Append current lines to the lines list
 
 
    cv.Copy(gray, prev_gray) #Put the current frame prev_gray
    prev_points = curr_points
 
    cv.ShowImage("The Video", frame)
    #cv.WriteFrame(writer, frame)
    c = cv.WaitKey(1)
    if c == 27: #Esc on Windows
        break